Many of the current shortcomings in diagnosis, prognosis, risk stratification and treatment of disease can be approached through the identification of the molecular mechanisms underlying a disease and through the discovery of nucleotide sequences (or sets of nucleotide sequences) whose expression patterns predict the occurrence or progression of disease states, or predict a patient's response to a particular therapeutic intervention. In particular, identification of nucleotide sequences and sets of nucleotide sequences with such predictive value from cells and tissues that are readily accessible would be extremely valuable. For example, peripheral blood is attainable from all patients and can easily be obtained at multiple time points at low cost. This is a desirable contrast to most other cell and tissue types, which are less readily accessible, or accessible only through invasive and aversive procedures. In addition, the various cell types present in circulating blood are ideal for expression profiling experiments as the many cell types in the blood specimen can be easily separated if desired prior to analysis of gene expression. While blood provides a very attractive substrate for the study of diseases using expression profiling techniques, and for the development of diagnostic technologies and the identification of therapeutic targets, the value of expression profiling in blood samples rests on the degree to which changes in gene expression in these cell types are associated with a predisposition to, and pathogenesis and progression of a disease.
Hematopoiesis is the development and maturation of all cell types of the blood. These include erythrocytes, platelets and leukocytes. Leukocytes are further subdivided into granulocytes (neutrophils, eosinophils, basophils) and mononuclear cells (monocytes, lymphocytes). These cells develop and mature from precursor cells to replenish the circulating pool and to respond to insults and challenges to the system. This occurs in the bone marrow, spleen, thymus, liver, lymph nodes, mucosal associated lymphoid tissue (MALT) and peripheral blood.
Precursor cells differentiate into immature forms of each lineage and these immature cells develop further into mature cells. This process occurs under the influence and direction of hematopoietic growth factors. When hematopoiesis is stimulated, there is an increase in the number of immature cells in the peripheral blood and in some cases, precursor cells are found at increased frequency. For example, CD34+ cells (hematopoietic stem cells) may increase in frequency in the peripheral blood with an insult to the immune system. For neutrophils, “band” forms are increased, for erythrocytes, reticulocytes or nucleated red cells are seen. Lymphocytes are preceeded by lymphoblasts (immature lymphocytes).
It may be an important clinical goal to measure the rate of production of blood cells of a variety of lineages. Hematological disorders involving over or under production of various blood cells may be treated pharmacologically. For example, anemia (low red blood cells) may be treated with erythropoietin (a hematopoietic growth factor) and response to this therapy can be assessed by measuring RBC production rates. Low neutrophils counts can be treated by administration of G-CSF and this therapy may be monitored by measuring neutrophil production rates. Alternatively, the diagnosis of blood cell disorders is greatly facilitated by determination of lineage specific production rates. For example, anemia (low RBCs) may be caused by decreased cellular production or increased destruction of cells. In the latter case, the rate of cellular production will be increased rather than decreased and the therapeutic implications are very different. Further discussion of the clinical uses of measures of blood cell production rates is given in below.
Assessment of blood cell production rates may be useful for diagnosis and management of non-hematological disorders. In particular, acute allograft rejection diagnosis and monitoring may benefit from such an approach. Current diagnosis and monitoring of acute allograft rejection is achieved through invasive allograft biopsy and assessment of the biopsy histology. This approach is sub-optimal because of expense of the procedure, cost, pain and discomfort of the patient, the need for trained physician operators, the risk of complications of the procedure, the lack of insight into the functioning of the immune system and variability of pathological assessment. In addition, biopsy can diagnose acute allograft rejection only after significant cellular infiltration into the allograft has occurred. At this point, the process has already caused damage to the allograft. For all these reasons, a simple blood test that can diagnose and monitor acute rejection at an earlier stage in the process is needed. Allograft rejection depends on the presence of functioning cells of the immune system. In addition, the process of rejection may cause activation of hematopoiesis. Finally, effective immunosuppressive therapy to treat or prevent acute rejection may suppress hematopoiesis. For these reasons, assessment of hematopoietic cellular production rates may be useful in the diagnosis and monitoring of acute rejection.
Current techniques for measuring cellular development and production rates are inadequate. The most common approach is to measure the number of mature cells of a lineage of interest over time. For example, if a patient is being treated for anemia (low red blood cell counts), then the physician will order a blood cell count to assess the number of red blood cells (RBCs) in circulation. For this to be effective, the physician must measure the cell count over time and may have to wait 2-4 weeks before being able to assess response to therapy. The same limitation is true for assessment of any cell lineage in the blood.
An alternative approach is to count the number of immature cells in the peripheral blood by counting them under the microscope. This may allow a more rapid assessment of cellular production rates, but is limited by the need for assessment by a skilled hematologist, observer variability and the inability to distinguish all precursor cells on the basis of morphology alone.
Bone marrow biopsy is the gold standard for assessment of cellular production rates. In addition to the limitations of the need for skilled physicians, reader variability and the lack of sensitivity of morphology alone, the technique is also limited by the expense, discomfort to the patient and need for a prolonged visit to a medical center. Thus there is a need for a reliable, rapid means for measuring the rate of hematopoeisis in a patient.
In addition to the relationship between hematopoiesis and variety of disease processes, there is an extensive literature supporting the role of leukocytes, e.g., T- and B-lymphocytes, monocytes and granulocytes, including neutrophils, in a wide range of disease processes, including such broad classes as cardiovascular diseases, inflammatory, autoimmune and rheumatic diseases, infectious diseases, transplant rejection, cancer and malignancy, and endocrine diseases. For example, among cardiovascular diseases, such commonly occurring diseases as atherosclerosis, restenosis, transplant vasculopathy and acute coronary syndromes all demonstrate significant T cell involvement (Smith-Norowitz et al. (1999) Clin Immunol 93:168-175; Jude et al. (1994) Circulation 90:1662-8; Belch et al. (1997) Circulation 95:2027-31). These diseases are now recognized as manifestations of chronic inflammatory disorders resulting from an ongoing response to an injury process in the arterial tree (Ross et al. (1999) Ann Thorac Surg 67:1428-33). Differential expression of lymphocyte, monocyte and neutrophil genes and their products has been demonstrated clearly in the literature. Particularly interesting are examples of differential expression in circulating cells of the immune system that demonstrate specificity for a particular disease, such as arteriosclerosis, as opposed to a generalized association with other inflammatory diseases, or for example, with unstable angina rather than quiescent coronary disease.
A number of individual genes, e.g., CD11b/CD18 (Kassirer et al. (1999) Am Heart J 138:555-9); leukocyte elastase (Amaro et al. (1995) Eur Heart J 16:615-22; and CD40L (Aukrust et al. (1999) Circulation 100:614-20) demonstrate some degree of sensitivity and specificity as markers of various vascular diseases. In addition, the identification of differentially expressed target and fingerprint genes isolated from purified populations of monocytes manipulated in various in vitro paradigms has been proposed for the diagnosis and monitoring of a range of cardiovascular diseases, see, e.g., U.S. Pat. Nos. 6,048,709; 6,087,477; 6,099,823; and 6,124,433 “COMPOSITIONS AND METHODS FOR THE TREATMENT AND DIAGNOSIS OF CARDIOVASCULAR DISEASE” to Falb (see also, WO 97/30065). Lockhart, in U.S. Pat. No. 6,033,860 “EXPRESSION PROFILES IN ADULT AND FETAL ORGANS” proposes the use of expression profiles for a subset of identified genes in the identification of tissue samples, and the monitoring of drug effects.
The accuracy of technologies based on expression profiling for the diagnosis, prognosis, and monitoring of disease would be dramatically increased if numerous differentially expressed nucleotide sequences, each with a measure of specificity for a disease in question, could be identified and assayed in a concerted manner. PCT application WO 02/057414 “LEUKOCYTE EXPRESSION PROFILING” to Wohlgemuth identifies one such set of differentially expressed nucleotides.
In order to achieve this improved accuracy, the sets of nucleotide sequences once identified need to be validated to identify those differentially expressed nucleotides within a given set that are most useful for diagnosis, prognosis, and monitoring of disease. The present invention addresses these and other needs, and applies to transplant rejection and detection of the rate of hematopoeisis for which differential regulation of genes, or other nucleotide sequences, of peripheral blood can be demonstrated.